Messages in this thread Patch in this message | | | Subject | [PATCH net v2] net: Fix suspicious RCU usage in bpf_sk_reuseport_detach() | From | David Howells <> | Date | Tue, 16 Aug 2022 14:26:19 +0100 |
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bpf_sk_reuseport_detach() calls __rcu_dereference_sk_user_data_with_flags() to obtain the value of sk->sk_user_data, but that function is only usable if the RCU read lock is held, and neither that function nor any of its callers hold it.
Fix this by adding a new helper, __rcu_dereference_sk_user_data_with_flags_check() that checks to see if sk->sk_callback_lock() is held and use that here instead.
__rcu_dereference_sk_user_data_with_flags() then calls that, supplying false as condition indicating only the RCU read lock should be checked.
Without this, the following warning can be occasionally observed:
============================= WARNING: suspicious RCU usage 6.0.0-rc1-build2+ #563 Not tainted ----------------------------- include/net/sock.h:592 suspicious rcu_dereference_check() usage!
other info that might help us debug this:
rcu_scheduler_active = 2, debug_locks = 1 5 locks held by locktest/29873: #0: ffff88812734b550 (&sb->s_type->i_mutex_key#9){+.+.}-{3:3}, at: __sock_release+0x77/0x121 #1: ffff88812f5621b0 (sk_lock-AF_INET){+.+.}-{0:0}, at: tcp_close+0x1c/0x70 #2: ffff88810312f5c8 (&h->lhash2[i].lock){+.+.}-{2:2}, at: inet_unhash+0x76/0x1c0 #3: ffffffff83768bb8 (reuseport_lock){+...}-{2:2}, at: reuseport_detach_sock+0x18/0xdd #4: ffff88812f562438 (clock-AF_INET){++..}-{2:2}, at: bpf_sk_reuseport_detach+0x24/0xa4
stack backtrace: CPU: 1 PID: 29873 Comm: locktest Not tainted 6.0.0-rc1-build2+ #563 Hardware name: ASUS All Series/H97-PLUS, BIOS 2306 10/09/2014 Call Trace: <TASK> dump_stack_lvl+0x4c/0x5f bpf_sk_reuseport_detach+0x6d/0xa4 reuseport_detach_sock+0x75/0xdd inet_unhash+0xa5/0x1c0 tcp_set_state+0x169/0x20f ? lockdep_sock_is_held+0x3a/0x3a ? __lock_release.isra.0+0x13e/0x220 ? reacquire_held_locks+0x1bb/0x1bb ? hlock_class+0x31/0x96 ? mark_lock+0x9e/0x1af __tcp_close+0x50/0x4b6 tcp_close+0x28/0x70 inet_release+0x8e/0xa7 __sock_release+0x95/0x121 sock_close+0x14/0x17 __fput+0x20f/0x36a task_work_run+0xa3/0xcc exit_to_user_mode_prepare+0x9c/0x14d syscall_exit_to_user_mode+0x18/0x44 entry_SYSCALL_64_after_hwframe+0x63/0xcd
Changes ======= ver #2) - Changed to suggestion from Hawkins Jiawei to have a ..._check() function and make the original a special case of that.
Fixes: cf8c1e967224 ("net: refactor bpf_sk_reuseport_detach()") Signed-off-by: David Howells <dhowells@redhat.com> cc: Hawkins Jiawei <yin31149@gmail.com> cc: Jakub Kicinski <kuba@kernel.org> cc: netdev@vger.kernel.org Link: https://lore.kernel.org/r/166064248071.3502205.10036394558814861778.stgit@warthog.procyon.org.uk # v1 ---
include/net/sock.h | 18 ++++++++++++++---- kernel/bpf/reuseport_array.c | 3 ++- 2 files changed, 16 insertions(+), 5 deletions(-)
diff --git a/include/net/sock.h b/include/net/sock.h index 05a1bbdf5805..6464da28e842 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -578,18 +578,22 @@ static inline bool sk_user_data_is_nocopy(const struct sock *sk) #define __sk_user_data(sk) ((*((void __rcu **)&(sk)->sk_user_data))) /** - * __rcu_dereference_sk_user_data_with_flags - return the pointer + * __rcu_dereference_sk_user_data_with_flags_check - return the pointer * only if argument flags all has been set in sk_user_data. Otherwise * return NULL * * @sk: socket * @flags: flag bits + * @condition: Condition under which non-RCU access may take place + * + * The caller must be holding the RCU read lock */ static inline void * -__rcu_dereference_sk_user_data_with_flags(const struct sock *sk, - uintptr_t flags) +__rcu_dereference_sk_user_data_with_flags_check(const struct sock *sk, + uintptr_t flags, bool condition) { - uintptr_t sk_user_data = (uintptr_t)rcu_dereference(__sk_user_data(sk)); + uintptr_t sk_user_data = + (uintptr_t)rcu_dereference_check(__sk_user_data(sk), condition); WARN_ON_ONCE(flags & SK_USER_DATA_PTRMASK); @@ -598,6 +602,12 @@ __rcu_dereference_sk_user_data_with_flags(const struct sock *sk, return NULL; } +static inline void * +__rcu_dereference_sk_user_data_with_flags(const struct sock *sk, uintptr_t flags) +{ + return __rcu_dereference_sk_user_data_with_flags_check(sk, flags, false); +} + #define rcu_dereference_sk_user_data(sk) \ __rcu_dereference_sk_user_data_with_flags(sk, 0) #define __rcu_assign_sk_user_data_with_flags(sk, ptr, flags) \ diff --git a/kernel/bpf/reuseport_array.c b/kernel/bpf/reuseport_array.c index 85fa9dbfa8bf..856c360a591d 100644 --- a/kernel/bpf/reuseport_array.c +++ b/kernel/bpf/reuseport_array.c @@ -24,7 +24,8 @@ void bpf_sk_reuseport_detach(struct sock *sk) struct sock __rcu **socks; write_lock_bh(&sk->sk_callback_lock); - socks = __rcu_dereference_sk_user_data_with_flags(sk, SK_USER_DATA_BPF); + socks = __rcu_dereference_sk_user_data_with_flags_check( + sk, SK_USER_DATA_BPF, lockdep_is_held(&sk->sk_callback_lock)); if (socks) { WRITE_ONCE(sk->sk_user_data, NULL); /*
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